Rotating Ballnut - design ideas

[Boyan Silyavski]

Please take some important notes:

In reality the screw is 25.00mm. And as all must be lined up to under 0.01mm/ 0.02mm could be felt as tightening at certain point/ so you can use 26mm of the center hole with no problem.


You must not make the parts smaller than the fitted part! |I have made that mistake and is impossible to fit correctly. Make all parts "press fit" 0.02mm bigger That means shaft must be 0.02mm bigger than inner bearing and bearing bed must be 0.02mm smaller


You know what i am saying? This is not a skateboard wheel. All your design is based on "esy to service", but in reality it must be based on "precision"




I dont know why the worry about the thickness. Let's speak in mm as this Imperial system gives me a headache

If i am not wrong ~ = The bearing has 35mm internal diameter. 22t pulley has ~35mm OD and ~31mm diameter on the tooth lowest point/35- 2x~2mm/ . So if the hole is 27mm that gives a 1 mm clearance from the 25mm ball screw, then (31-27 ) /2 = 4mm wall at the pulley thinnest point, so whats the big deal?
Even so where the tooth is its thicker by 2mm so...???

[m_c]

I dont know why the worry about the thickness. Let's speak in mm as this Imperial system gives me a headache

If i am not wrong ~ = The bearing has 35mm internal diameter. 22t pulley has ~35mm OD and ~31mm diameter on the tooth lowest point/35- 2x~2mm/ . So if the hole is 27mm that gives a 1 mm clearance from the 25mm ball screw, then (31-27 ) /2 = 4mm wall at the pulley thinnest point, so whats the big deal?
Even so where the tooth is its thicker by 2mm so...???

I was just going by the drawing, which put the thinnest point at 0.0421", or 1.06mm.
It probably would be ok in aluminium, but as I mentioned, by the time you allow for all the forces likely to be acting on the shaft, it is quite a highly stressed part. I wouldn't be comfortable with it unless a FEA showed a good bit of safety margin, but it seems to be a lot of work just to avoid boring out a pulley.

[mutzy]

Happy New year to all coming up. May we all have a great year of designing and learning.

Boyan, I did reset the OD of the shaft back to 35 mm + .02mm on both sides of the gear.
The inner diameter hole was set to 26 mm.

The pulley is 33.899 mm outer, 29.533 at the tooth lowest point
Wall thickness from lowest tooth point to inner dia is ~1.85 mm.

Yes M_C, I was doing this to eliminate the pulley step and as Jonathan posted earlier to lower the moment of inertia. (hope i didn't open another can of worms by saying that.LOL
mutzy

[m_c]

In the grand scheme of things, is the amount of inertia saved likely to make that much difference? Is a couple hundred grams of pulley, going to be that significant in relation to a 30KG+ gantry?

[mutzy]

Boyan, If you could look at this, I would appreciate any feedback. thank you

MutzyNewZip.zip

[mutzy]

Hey Boyan, does this look good now? Can I send you my cad file to take a look at just to see if everything looks ok?

Mutzy

[reefy86]

i have these on my list for the 4000mm ballscrew lengths but would you say i would also need them for 1800mm lengths?

[mutzy]

Reefy86, how are you? I am no expert in this forum like Boyan, M_C and Jonathan are. They truly understand the science behind the build. I was told once that once you start geting more than about 1574.8 mm the possible whipping action of the ballscrew may have an effect on the life of the bearings... take this into consideration and maybe the professionals could answer the question more directly. Mutzy

[reefy86]

That's what i was thinking so in general then i may need 3 of these ordering which i know these are not cheap but what is lol

[magicniner]

If it's only whipping in the ball screws and not rotational mass there have been some very elegant, low cost solutions to that,

- Nick